This invention relates generally to a method and apparatus for atomizing a liquid. More specifically, this invention is concerned with an easily cleaned and/or serviced atomizing nozzle which finds particular utility with difficult-to-handle liquids and which is capable of atomizing the liquid into uniform droplet sizes.
The process of atomization is of noteworthy importance in several branches of engineering including the chemical industry for operations involving drying, evaporating and absorption, the coating industry wherein paint is applied by a spraying technique, the agriculture industry for crop stimulation and protection, etc. Atomizing of a liquid is typically accomplished by forcing the fluid under pressure through a nozzle into the atmosphere where the liquid contracts into droplets.
Nozzle designs may often assume the configuration of a cylindrical nozzle body which is covered at one end by a transversely extending orifice plate or disc. The disc is typically releasably affixed to the end of the nozzle body by a conventional threaded ring connector. An illustration of such a nozzle configuration is disclosed, inter alia, in Vehe et al. U.S. Pat. No. 3,679,137 issued July 25, 1972 and assigned to the assignee of the subject application. The disclosure of this Vehe et al. patent is hereby incorporated by reference as though set forth at length.
While nozzle configurations, such as disclosed in the Vehe et al. patent, have been utilized with at least a degree of acceptance in the past, room for significant improvement remains.
More particularly, conventional nozzle orifice discs are often fabricated from somewhat thick brass sheet stock for considerations of strength and corrosion resistance. Apertures within the disc are often accurately bored with a diameter of a few hundredths inch or less. Accordingly, conventional nozzle orifice discs are somewhat expensive to manufacture.
Moreover, in many instances a "fan" spray pattern is desired. Such a spray pattern may be effected by forming a circular nozzle disc with a disc shape configuration and boring one or more rows of radially extending apertures through the disc-shaped disc. Accurately boring radial apertures merely heightens the previously noted manufacturing intricacy and expense.
During an atomizing operation, fines suspended within the liquid medium being dispensed tend to clog the aperture or apertures in the disc. Operational clogging dictates "on the job/in the field" shutdowns for servicing. In this regard an operator would typically release pressure from the fluid being dispensed and remove the threaded attachment collar to free the orifice disc for manual inspection and cleaning. It will be appreciated by those skilled in the art that during the foregoing procedure liquid within the nozzle body will in all likelihood spew onto the hands and forearms of the operator. In some instances, this occurence is merely objectionable and disconcerting. In other instances, it becomes mandatory that an operator's hands are properly isolated from direct contact with the liquid being atomized. Examples of such liquids would include vehicles carrying indelible pigments or an agricultural control fluid which is highly toxic by inhalation and/or skin absorption. A specific example of the latter is paraquat, which is a generic name for a 1,1'-dimethyl-4-4'-bipyridinium salt. Paraquat is a yellow solid herbicide which is soluble in water and is highly toxic by skin absorption.
An associated difficulty may be occasioned if it is desired to alter a spray flow pattern. In this regard, the system is again typically shut down and the orifice disc is replaced with one having a more appropriate aperture pattern. In making such a changeover, operator contamination may again present a difficulty as outlined above.
Another significant concern in atomizing operations is the tendency of atomized fluids to contract into droplets of variant sizes. As an example, conventional spray nozzles which would be designed to produce droplets having a mean diameter of 150 microns will also typically generate droplets ranging in size from 1 to 2 microns up to 300 or 400 microns in diameter. While the foregoing range in droplet sizes may be acceptable in some applications, in many instances finer control of droplet size during atomization would be highly desirable.
In this latter connection in large scale agriculture, it has been found in dispensing herbicides and pesticides that fine droplet sizes tend to be blown or drift away from a desired zone of application while very large droplet sizes tend to coalesce and drip from leaf surfaces without producing a desired biological action. In a similar vein in the spray painting industry, very fine droplets tend to be drawn into an overhead exhaust system while very large droplets tend to form undesirable globules upon a coated surface.
In the past, at least one device has been found to provide significant potential with respect to controlling droplet size during an atomization process. In this connection, attention is re-invited to the previously identified Vehe et al. patent. In this Vehe et al. patent, a jet stream vibratory atomizing device is disclosed wherein a magnetostrictive shaft is mounted within the interior of a nozzle body and functions to induce vibrations within a liquid dispensed through an orifice plate to break a liquid into uniform droplet sizes downstream of the orifice plate.
While the Vehe et al. structure offers considerable potential with respect to accurately dispensing a liquid, room for significant improvement remains.
It has been found that placement of a magnetostrictive vibratory shaft within the interior of a nozzle body represents at least a potential sealing problem as well as providing an obstruction to the flow of fluid through the nozzle body. Additionally, it would be desirable to enhance droplet size formation and/or to minimize energy input while maintaining acceptably accurate droplet control.
The problems suggested in the preceding are not intended to be exclusive but rather are among many which may tend to reduce the effectiveness of prior art atomizing assemblies. Other noteworthy difficulties may also exist; however, those presented above should be sufficient to demonstrate that atomizing methods and apparatus appearing in the prior art have not been altogether completely satisfactory.